Systems and methods for measuring respiratory biometrics

ABSTRACT

Some embodiments are directed to a self-contained breathing mask for measuring and monitoring the breath of a human subject. The mask may be lightweight, self-contained, and physically untethered to any test or measurement equipment, providing the subject full mobility, and allowing him/her to perform almost any daily activity during use. The mask may include integrated sensors for measuring properties of the subject&#39;s breath, over any length of time, providing respiratory information like breath count, rate and volume, oxygen consumption, and carbon dioxide production, as well as various biometric information.

RELATED APPLICATIONS

This application is a continuation of commonly assigned U.S. patentapplication Ser. No. 16/984,675, filed Aug. 4, 2020, entitled “Systemsand Methods for Measuring Respiratory Biometrics,” bearing AttorneyDocket No. V0340.70001US01, which claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No. 62/904,762, filedSep. 24, 2019, entitled “System for Monitoring Human Breath in DailyLife,” bearing Attorney Docket No. V0340.70001US00. Each of thedocuments referenced above is incorporated herein by reference in itsentirety.

TECHNICAL FIELD

Embodiments of the present disclosure generally relate to systems,methods and devices for collecting, analyzing and utilizing respiratory,physiological, metabolic or biometric data.

BACKGROUND

Respiratory air flow volume and composition is rich with biometric anddiagnostic information. One example is pulmonary function and thechanges in pulmonary function for any individual in response to changesin circumstances, activity or disease. Another example is metabolicinformation that can be reflected qualitatively and quantitatively bymeasuring the exchange of gases, and the correlation of this gasexchange to health, nutrition, activity or other circumstances.

SUMMARY

Some embodiments of the invention are directed to a system, configuredto be worn by a user substantially on his/her head, for gatheringrespiratory information about the user. The system comprises a mask anda sensing module. The mask comprises a shell and a seal. The seal isformed of a pliable material arranged to contact a face of the user andto substantially circumscribe an area of the face when the mask is wornby the user. The area of the face includes a mouth of the user and abase of a nose of the user. The seal and the shell substantially enclosean interior space about the area of the face and substantially separatethe interior space from an ambient space. The shell comprises aplurality of breathing apertures configured to allow air to flow betweenthe interior space and the ambient space. The sensing module comprises ahousing arranged for attachment to the mask. The sensing modulecomprises gas sensors, air pressure sensors, electronic components, anda battery for powering the gas sensors, the air pressure sensors and theelectronic components. The sensing module has a sensing zone with an airflow path from the interior space. The gas sensors are in fluidcommunication with the sensing zone, and are configured to measure acomposition of air exhaled by the user. The air pressure sensors areconfigured to measure a pressure difference between the interior spaceand the ambient space. The electronic components are configured toreceive data from the gas sensors and the air pressure sensors, and totransmit first information to at least one external device. The firstinformation comprises the received data and/or a result of processing atleast a portion of the received data, the processing comprisingdetermining one or more of an inhalation air flow and an exhalation airflow based at least in part upon the measured pressure differencebetween the interior space and the ambient space.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-B are schematic illustrations of a representative systemimplemented in accordance with some embodiments of the presentdisclosure. FIG. 1A shows front and side views of the representativesystem, and FIG. 1B shows the system worn on a user's face.

FIGS. 2A-B are schematic illustrations of a representative sensingmodule detached from the mask, in accordance with some embodiments ofthe invention. FIG. 2C illustrates one embodiment showing how a user canremove the module while wearing the mask.

FIGS. 3A-B depict a representative internal layout of an exemplarysensing module implemented in accordance with some embodiments, withsome elements omitted to provide better visibility of certain sensors.For example, in FIG. 3A the ports of the differential pressure (DP)sensor are visible, and in FIG. 3B one of the tubes (168) attached tothe interior-pressure port is shown.

FIG. 4 is a schematic illustration of a cross section of arepresentative sensing module oriented so that the interior space of themask is above the module in the example shown.

FIG. 5 is a schematic cross-section of a representative sensing module,comprising a vestibule residing between the mask and the sensing spacein the example shown.

FIGS. 6A-B illustrate how air may flow through the mask duringbreathing, in accordance with some embodiments. FIG. 6A depictsinhalation, where air flows inward through the mask apertures inresponse to a negative differential pressure inside the mask relative tothe ambient.

FIG. 6B depicts exhalation, where flow and differential pressure arereversed.

FIGS. 7A-C are schematic illustrations of a representative apparatus andtechnique for SEAS (Separated Exhaled Air Sensing), in accordance withsome embodiments of the invention.

FIG. 8 is a schematic illustration of a representative apparatus andtechnique for MAS (Mixed Air Sensing), in accordance with someembodiments of the invention.

FIGS. 9A-D depict non-limiting examples of different mask and apertureconfigurations. It will be clear to a person skilled in the art thatthere are limitless other design choices possible, not only for theapertures but for the mask, the sensing module and the straps.

DETAILED DESCRIPTION OF THE INVENTION

The Applicant has appreciated that measuring the volume and compositionof respiratory air flow is a known medical diagnostic technique, butdoing so is cumbersome and expensive, requiring the subject to betethered to analytic instrumentation that is either stationary orunwieldy. The Applicant has also recognized that this makes itimpractical to measure such biometrics continuously over a long stretchof time, or to do so in the course of daily life, as opposed to in alimited diagnostic setting, such as in a medical facility or sportslaboratory. While some devices can be carried to monitor outdoorathletic activity, these require attachment—by tubes or wires—toinstrumentation that is carried by the user, and remain too cumbersomeand expensive for widespread, daily use.

Wearable devices for collecting biometric data have become increasinglypopular for use by consumers in their daily life. Some are designed togather biometric data regarding the individual wearing them, for exampleusing motion sensors or contact electrodes. The Applicant has alsorecognized that some keys to the widespread adoption of wearable devicesinclude a small form factor, comfort and affordability. The Applicanthas further appreciated that, to date, there is no wearable device formeasuring breath volume and composition having these qualities.

Some embodiments of the invention are directed to systems, apparatusesand methods for measuring and monitoring a person's breath, using anovel type of self-contained breathing mask with integrated sensors. Insome embodiments, the mask may be extremely light, and untethered to anytest or measurement system—neither electrically nor via tubes—andutilize miniature battery powered sensors and wireless electronics tomeasure properties of breath continually over any length of time, whileallowing the user full mobility and the ability to perform almost anyactivity while unencumbered and minimally inconvenienced by the device.In some embodiments, data which is collected over periods of time mayprovide respiratory information like breath count, rate and volume, aswell as oxygen consumption and carbon dioxide (CO₂) production. Thesedata may be processed to produce information relating to metabolic data,like energy (calories) consumed, or to estimate the fraction of suchcalories obtained from metabolizing carbohydrates vs. fats, since thetwo have different CO₂-to-oxygen respiratory exchange ratios. In someembodiments, one or more sensors may enable medical or physiologicaldiagnostics and tracking biometrics.

In some embodiments, the system comprises a partially rigid mask thatcovers the mouth and nostrils, with breathing apertures in the mask andone or more detachable sensing modules. The system may continuallydetermine instantaneous respiratory air flow, such as by measuring apressure difference between the mask interior and the ambient air. Thesystem may measure the composition of exhaled air in terms of oxygen andCO₂ concentrations. Any data that is gathered, generated and/or derivedmay be conveyed by wireless connection to an external receiving device,such as a mobile phone, or any other suitable computing system(s). Theconvenience and low cost of such a system may enable respiratory datacollection in day to day life, with valuable insight on health anddisease, nutrition, metabolism, activity, athletic performance, sleep,etc. Data collected by the system may also be used for medicalmonitoring, diagnostics, and/or sports medicine. In some embodiments,data gathered by plural systems associated with individual humansubjects may provide a research tool, for example allowing the humansubjects to be monitored as part of a study.

FIGS. 1A-B depict a representative system (100) comprising an exemplarybreathing mask (110) configured to be worn by a user, substantially onhis/her head. In the representative system 100 shown, mask 110 comprises(i) a firm shell (111) that is designed to essentially maintain itsshape when the mask is worn, and (ii) a soft, flexible or otherwisepliable material, also referred to as a cushion (112), along the edgesof the mask. In the example shown, the cushion is configured to contactthe user's face and substantially circumscribe an area of the faceincluding the mouth and the base of the nose or the nostrils, whileconforming to the facial contours, thus substantially preventing airfrom flowing through gaps between the mask and the skin. When applied tothe face (FIG. 1B), example mask 110 may substantially enclose aninterior space (120) contained between the mask and the face. The spaceoutside the mask and immediately adjacent to it are referred to hereinas the ambient space (125). The mask 110 is further configured with aplurality of geometrically defined apertures or perforations (130)allowing inspired (inhaled) air to flow from the ambient space 125 tothe interior space 120, or allowing expired (exhaled) air to flow fromthe interior space 120 to the ambient space 125. In some embodiments ofthe invention, a subject's breath does not need to flow through anytubes or conduits for flow rate to be correctly quantified.

It should be appreciated that the mask 110 depicted in FIG. 1 is merelyone example, and that a mask implemented in accordance with embodimentsof the invention may include any of numerous combinations of elements(only some of which are shown) and/or configurations thereof. As but oneexample, there may be a wide variety in the design of the apertures interms of their size, shape, number and location on the mask. In someembodiments, the operation of the system may dictate at least some ofthe elements and/or configurations thereof, but in some embodiments, thepresence and/or configuration thereof may be dictated (at least in part)by other considerations. Some representative operational considerationswhich may influence design choices are disclosed below.

In certain embodiments, one or more apertures may be configured with“one-directional” flow elements to allow inhalation-only orexhalation-only through these apertures, which are referred to herein as“inhalation apertures” or “exhalation apertures,” respectively. In anon-limiting example, a mask may have a plurality of ordinary apertures(130) allowing air flow in both directions, and several additionalinhalation apertures (134), to reduce air flow resistance of the maskduring inhalation, while maintaining a somewhat higher resistance forexhalation. Some benefits of this arrangement are described below.

Passive one-directional flow valves are known. One example comprises aflexible cover (a “flap”) configured to seal the aperture from one side.Positive air pressure from one direction pushes the flap open and allowsflow, while pressure from the other direction pushes the flap againstthe surface, tightening the seal and obstructing flow. Of course, a maskimplemented in accordance with embodiments of the invention may includeany suitable type(s) of selective flow element(s). Some non-limitingexamples are described below.

In the example shown, mask 110 includes a sensing module or subassembly(150) which houses sensors and/or other electronic components. In someembodiments, the sensing module may be contained in a housing that iseasily attachable to and/or detachable from the mask. In someembodiments, a plurality of separate sensing modules may be attached tothe mask.

FIG. 2A depicts an embodiment of a mask (110) and a sensing module (150)showing the sensing module separated (e.g., detached) from the mask. Insome embodiments the housing mates with a feature in the mask (152)which helps to set its position. This can be any feature including butnot limited to an opening, a recess, a cavity and a receptacle. In someembodiments the inserted module can be secured in place with the aid ofattaching elements, including but not limited to magnets, adhesives, andrigid or flexible mechanical features (156) for holding the housing inplace. In some embodiments, the mask is configured with an air-permeableaperture (155) at the location of the module that can allow fluidcommunication between the mask interior and the module. FIG. 2B showsthe module housing as a separate object after removal. FIG. 2C shows howa user can remove and replace the module while wearing the mask

In some embodiments, the ability to remove the sensor module from themask has several possible roles, including but not limited to (a)allowing cleaning or disinfecting the mask, such as with water,detergents, radiation or elevated temperatures, which would damagesensors or electronic components if the module is not removed from themask before such cleaning; (b) changing or replacing the mask from timeto time without necessarily requiring multiple modules, and (c) sharinga module among several users, each equipped with their own mask. Itshould be appreciated, however, that in some embodiments, the sensingmodule may not be detachable from the rest of the mask, and that in someembodiments, only a portion of the sensing module (e.g., certaincomponents thereof) may be detachable from the rest of the mask.Embodiments of the invention are not limited to being implemented in anyparticular way.

The components of the sensing module can comprise a plurality ofsensors, including but not limited to any of pressure sensors, gassensors, temperature sensors, chemical sensors, electromechanicalsensors, optical sensors, accelerometers, and/or humidity sensors. Thesensing module may also include one or more batteries and one or moreelectronic circuits configured to receive sensor readings and/orcommunicate (e.g., wirelessly) with one or more external systems. FIG.3A shows a schematic view of a representative sensor module 150implemented in accordance with embodiments of the invention. Therepresentative sensor module 150 shown comprises a differential pressuresensor (160), a gauge- or barometric-pressure sensor, a humidity sensor(164), a carbon dioxide (CO₂) sensor (165) and an oxygen (02) sensor(166). The system may also, or alternatively, comprise multipletemperature sensors. Some commercially available gas sensors have“built-in” temperature sensors or humidity sensors, thus potentiallyeliminating the need to incorporate these as separate sensors. Theoperation of this embodiment will be explained here in further detail;it will be understood, however, that this combination of sensorsrepresents a non-limiting example. It should be appreciated that asensor module 150 may comprise any suitable number and/or type ofsensors. A sensor module implemented in accordance with embodiments ofthe invention may not include all of the sensors shown in FIGS. 3A-3B,or may include sensors other than those which are depicted in FIGS.3A-3B. Sensor module 150 may be implemented and configured in any ofnumerous ways.

In some embodiments, a differential pressure (DP) sensor may beconfigured with two inlets or ports, shown as 161 and 162 in FIG. 3A. Inthe example shown, each port is in the form of a short tubular openingextending from the main sensor body. Many differential pressure sensorsare available with suitable performance characteristics, such as theTrustability® HSC series available from Honeywell Corp. or the SDP31series from Sensirion AG (Switzerland), and similar products from NXPSemiconductors (Netherlands), Amphenol Corp., Merit Sensor, and others.In some embodiments the DP sensor is configured so that one of thesensor's inlets is in fluid communication with the interior space, whilethe other is in fluid communication with the ambient space. Such fluidcommunication may, for example, be facilitated by a suitable conduit.The conduit can comprise any suitable type, including but not limited toone of flexible tubing, rigid duct, a monolithic part of the housing, orany combination of these. In embodiments that use such a conduit, theopen end of the conduit is referred to herein as the “port extension.”In some embodiments, the measured pressure may be representative ofpressure at the port extension. In the example depicted schematically inFIGS. 3A-3B, the DP sensor has one port (161; FIG. 3A) in communicationwith the interior space through a conduit (168; FIG. 3B) and acorresponding aperture in the housing; and the other port (162; FIG. 3A)in fluid communication with the external ambient air through a separateconduit (not shown). In this respect, it should be appreciated that incertain embodiments (e.g., those in which the DP sensor is located in apart of the module that is already in fluid communication with one ofthese spaces—interior space or ambient air), a conduit may not benecessary for a corresponding port.

In some embodiments the instantaneous rate of air flow through theapertures can be determined by measuring DP between the interior spaceand the ambient air. In doing so, the system may continuously trace arespiratory flow rate (FF) over time. The conversion of DP to FF may beinfluenced by, for example, the mask structure, including but notlimited to the configuration of apertures, as well as the location ofthe DP sensor port extensions. Given this, in some embodiments, thelocation of these port extensions may be fixed, so as to produce apredictable and consistent relation between the FF and DP.

Some embodiments may include features designed to account for variationsin air flow patterns in the mask interior. In this respect, even for thesame person and the same total air flow there can be different flowpatterns, for example between nasal vs oral exhalation, or even withinoral exhalation with varying positions of the mouth. Moreover, differentindividuals will often have different facial features that can affectflow patterns. In some subjects, flow patterns can vary more stronglynear the mouth and nose. As such, some embodiments may include maskapertures positioned away from the center, and therefore away from themouth and nose, namely closer to the edges of the mask, such as toreduce flow pattern variations. For example, in some embodiments, theexhalation apertures may be positioned closer to the perimeter or edgesof the mask. In some embodiments, an interior sensing port extension maybe positioned closer to the edges of the mask. In some embodiments, theinterior-space pressure sensing port may be shielded from pressure-flowidiosyncrasies like laminar flow by locating the port inside the modulein a section that is in fluid communication with the interior space butshielded from direct flow. Of course, the system is not limited toemploying apertures, a sensing port extension, and/or an interior-spacepressure sensing port residing in any particular location. In someembodiments, one or more physical features including but not limited toscreens, barriers and obstructions may be configured to deflect exhaledair from flowing directly to apertures or to sensors.

Embodiments of the invention may employ any suitable number of sensorsof a particular type. As one example, in some embodiments, more than onepressure sensor may be installed. For example, some embodiments maycomprise a gauge pressure sensor to measure the absolute or barometricpressure P. The barometric pressure can be used alongside temperature Tto correctly convert air volume to mass or to “standard volume” (e.g.standard liters per minute, SLPM). Such conversion requires knowledge ofT and P.

As another example, in some embodiments, multiple DP sensors may beused. Employing multiple DP sensors may enable DP to be sensed atmultiple locations in the interior space, which may reduce or mitigateflow pattern variations. In some embodiments, module 150 may comprisemultiple DP pressure sensors having different ranges and sensitivities,which may (as described in more detail below) afford better accuracy anddynamic range than a single DP sensor.

Some embodiments may employ a compact and low-power oxygen sensor (166)so as to minimize weight, size and battery power consumption. Similarconsiderations apply to a CO₂ sensor and other gas sensors. There areseveral suitable technologies with commercially available sensors havingthese characteristics. Miniature CO₂ sensors using techniques includingbut not limited to, non-dispersive infra-red (NDIR) adsorption,photoacoustic effect, and thermal conductivity, are commerciallyavailable from multiple vendors in very small form, usually weighing nomore than a few grams. Compact oxygen sensors using techniques includingbut not limited to electrochemical sensors and fluorescence quenchingare also available in low cost, low power and light weight forms. Inspite of these advantages, embodiments of the invention are not limitedto using sensors (oxygen sensors or otherwise) having any particularoperating principle, form factor, cost, weight and/or power consumptioncharacteristics.

Certain embodiments have multiple sensors of a similar type, for exampletwo or more oxygen sensors, CO₂ sensors, humidity, pressure, ortemperature sensors. Sensors may be duplicated for any number ofreasons, including but not limited to the ability to provide higheraccuracy by combining (e.g., averaging) readings from multiple sensors,and/or providing redundancy or back up in case a certain sensor fails.

In some embodiments, one or more components in the sensing module may bemounted on one or more circuit boards (170), which can be rigid,flexible, or possess a combination or rigid and flexible parts. Therepresentative module shown in FIGS. 3A-3B also comprises one or morebatteries (171). In some embodiments a battery may be rechargeable, andthe system may comprise an external electrical port for charging thebattery. In some embodiments, an electrical port can serve additionalpurposes, including but not limited to uploading or downloading softwareor data. The module further comprises electronic circuit componentsincluding a wireless communications module (172), and a microprocessor,described in more detail further below. In some embodiments themicroprocessor is an integrated part of the communications module.

In some embodiments the sensing module may be divided into a pluralityof chambers or compartments, and each of these compartments may besealed or in fluid communication with other spaces, such as the interiorspace, the ambient air, or another compartment. In certain embodiments,some components which include components such as a microprocessor,battery, radio transmitter and digital memory may reside in acompartment that is sealed from exhaled air flow. Of course, a sensingmodule implemented in accordance with embodiments of the invention neednot include plural chambers.

Sensing Zone and Optional Vestibule. FIG. 4 shows a schematic crosssection of a representative sensing module comprising an oxygen sensor(466), CO₂ sensor (465), humidity (467) and temperature (468) sensorsconfigured to measure properties of exhaled air. The sensing module isarranged so that these sensors probe the air in a “sensing zone” (410)that receives exhaled air from the mask interior (400) when the mask isworn. In some embodiments, these sensors may be in fluid communicationwith (e.g., reside at least partially within) the sensing zone. While insome embodiments the sensing zone may comprise the entire volume of themodule, in the example shown, the sensing zone is a confined chamber orsection within the module. An inlet (440) provides an air flow pathallowing exhaled air to enter the sensing zone. The sensing zone inlet(440) may, for example, include a filter to prevent or reduce theingress of particles, debris, water condensation or other unwantedcomponents into the sensing zone itself, while allowing gases to enter.Of course, an air flow path allowing exhaled air to enter the sensingzone need not be provided using an inlet which includes a filter, andany suitable arrangement may be used to provide such an air flow path.In the example shown, sensing zone 410 includes an outlet (450) enablingair to flow through the space.

Although only a single sensing zone is shown in FIG. 4, in someembodiments, a plurality of sensing zones may reside in a sensingmodule. For example, each sensing zone may include different sensorscorresponding to that zone. For example, each different sensing zone mayreceive different amounts of air flow, which can be influenced by any ofthe apertures, valves or conduits directing air to the zone.

While in some embodiments air may flow directly from the interior spaceto the sensing zone, some embodiments may provide for an intermediatespace along a flow path from the interior space to the sensing zone,which is depicted schematically in FIG. 5 and referred to herein as avestibule. In some embodiments which include a vestibule, exhaled aircan only reach the sensing zone by first entering the vestibule, andthen flowing from the vestibule to the sensing zone. Some potentialbenefits of the vestibule are described in further detail below. Itshould be appreciated that although the example shown in FIG. 4 includesa single sensing zone, not all embodiments may include a sensing zone,or even a small number of sensing zones, but instead may include sensorsinterspersed throughout the system. Embodiments of the invention are notlimited to sensors being physically arranged and/or configured in anyparticular way.

System Operation—Air Flow Measurement. We now turn to explain theoperation of some embodiments in measuring respiratory volumes and flowrates. The operation of the system in this embodiment can be explainedwith the help of FIGS. 6A and 6B, showing inhalation and exhalation,respectively. When the user inhales, low pressure in the lungs pulls airthrough the mask apertures. If the mask is properly attached, theinhaled ambient air flows substantially through designated breathingapertures rather than through gaps between the mask and the face. Therate of air flow through the mask apertures is determined by a lowerpressure in the mask interior relative to the exterior ambient pressure,which is of course created by the lungs and the respiratory muscles.This pressure difference is detected by the DP sensor, which, in someembodiments, has one port inside the mask and the other outside themask.

Similarly, when the user exhales, high pressure is produced by the lungsand the air flows out through the designated apertures to the ambient.The air flow is induced and determined by a pressure difference DP thatis caused by the (even higher) pressure in the lungs. It is measured bythe DP sensors described earlier, and the measured value is received bythe electronic circuit, and may be processed, stored and/or transmitted.

The pressure sensor(s) effectively measures this pressure differencebetween the interior mask pressure, P_(i), and the ambient pressureoutside of the mask, P_(a).

DP=P _(i) −P _(a)

A consistent mathematical relationship exists between the respiratoryair flow FF and the DP measurement. This pressure-velocity relationshipcan be approximately linear at low rates, and in any case a fixedproperty of any particular mask & aperture design. It need not besymmetrical or precisely linear, but as long as it is consistent,monotonic and well calibrated, it can be used to convert DP readings toFF for that particular mask design.

Typical human tidal breathing comprises approximately 12-15 inhalationand exhalation cycles per minute, and each cycle for an average adultmale is around 0.5 liters of air. However, breath frequency and volumecan be much higher under physical exertion. To measure breath volumeaccurately, the flow—hence the DP—should be measured in sufficientlyhigh time resolution so as to capture the oscillating changes in flowrate with adequate fidelity. In other words, the DP readings should berecorded at high reading rate relative to the breathing frequency.Fortunately, typical DP sensors have reading rates much faster than eventhe most elevated human breathing rate. Sensors specified at 1millisecond reading time, namely a 1 kHz rate, are fairly common. Insome embodiments the DP sensor values are recorded at a frequencybetween 10-100 readings per second, which is often suitable. In someembodiments, DP sensor readings are taken at a frequency between100-1000 per second. In some embodiments readings are taken at a rateslower than 10 per second. In some embodiments, readings are taken at arate higher than 1000 per second. In some embodiments readings are takenat a variable frequency, based on the read values and their rate ofchange.

In some embodiments the exact relationship between DP and FF can beestablished by testing or simulation and then stored and used as aconversion table, a parametric formula, or a hybrid conversion that usesa plurality of piecewise conversion formulas, each applying to a certainrange of values of DP. In the case of a table, values that are notspecifically represented on the table can be converted by interpolationbetween available values or rounded to the nearest available value. Insome embodiments a parametric formula can be as simple as linearconversion

FF=a ₁ DP

or a power series expansion such as

FF=a ₁ DP+a ₂ DP ² +a ₃ DP ³+ . . .

Where a₁, a₂ etc. are the conversion coefficients.

The conversion of DP to FF can be performed by the sensing module,and/or after transmission (e.g., by a receiving device). If theconversion is performed by the sensing module, in some embodiments amicroprocessor in the sensing module may perform the conversion, such asusing a conversion table, or coefficients, stored in memory. In someembodiments, the DP readings themselves may be transmitted—directly orindirectly—to a separate computing system, the latter being programmedto perform the conversion and supplied with the required tables,coefficients or formulas.

In some embodiments, frequent recalibration of the zero point of a DPsensor can reduce measurement errors. Such recalibration can beperformed by measurement of the DP when there is no air flow at all,such as when the mask is not worn or the module is detached from themask, as shown schematically in FIG. 2.

In some embodiments the size, number and configuration of the aperturesmay affect DP during breathing. As a non-limiting example, if theapertures are relatively smaller or fewer, then DP readings might belarger and easier to measure, but breathing may be relativelyrestricted, especially under exertion and athletic activity. Bycontrast, if the apertures are relatively wide or numerous, breathingmay be easier, but DP values may be smaller and more difficult tomeasure accurately. As such, DP reading considerations may influence thedesign of the apertures.

Variable Apertures. In some embodiments, variable apertures can be usedto allow for different operating modes. In a non-limiting example, oneor more apertures can be configured with a cover or seal that can beopened manually by the user or electronically by the module. When thevariable apertures are closed, the system may be better suited forordinary breathing rates, providing relatively higher resistance andtherefore easier to accurately measure DP at low air flow rates.Conversely, when some or all of the variable apertures are open, thesystem may be better suited for higher breathing rates, for exampleduring exercise or hard work.

In some embodiments, some or all of the variable apertures may allow forplural settings, including settings labeled as open/closed, high/low, orusing any other suitable nomenclature. In some embodiments the systemenables more than two settings or operating states. These multiplestates may be realized, for example, by partially opening or closingcertain apertures. In some embodiments, multiple operational states maybe realized using a multistate seal on one or more apertures. Anon-limiting example of a seal is a sliding cover that can graduallycover or reveal a portion of an aperture.

In some embodiments, some or all of any variable apertures may becontrolled physically by the user, such as by moving or removingappropriate covers as needed. In some embodiments, some or all of anyvariable apertures may be activated electronically by the system. Insome embodiments the system can be programmed to change the settings forone or more of any variable apertures in response to a user request. Insome embodiments the system may modify settings for one or more of anyvariable apertures based on circumstances (e.g., detected by thesystem). In a non-limiting example, the system may modify settings forone or more of any variable apertures in response to a measured flowrate or a breathing frequency.

In some embodiments with variable apertures, the conversion of DP to FFis informed by the settings of certain apertures and the systemregisters the latter to properly calculate FF. In some embodiments, thesettings may be provided to the system by the user. In some embodimentsthe settings determined or detected independently by the system throughany suitable means, including but not limited to magnetic, mechanical oroptical sensors.

In some embodiments, if the mask does not seal well against the face,air can flow through gaps between the mask and the face duringinhalation or exhalation, which is referred to herein as leakage. Suchleakage may undermine the equality between the aperture air flow and thetotal respiratory air flow. The cushion of the mask may play animportant role in sealing and minimizing leakage. Some designs may beprone to leakage in one direction (inhalation or exhalation) but notboth; since the volume of inhaled and exhaled air are similar, in someembodiments sealing that is effective for only one direction maytherefore be sufficient.

In some embodiments, only exhaled air flow rate may be recorded and usedfor computing biometric quantities. Such embodiments may benefit fromadding one-way inhalation apertures that further reduce inhalationpressure differentials, thereby increasing inhalation comfort withoutundermining flow measurement accuracy at low exhalation rates. In someembodiments, only inhaled air volume may be recorded and used forcomputing biometric quantities, with parallel benefits. In someembodiments, both inhaled and exhaled air may be used for computingbiometric quantities.

Alternative Techniques to Measure Air Flow. It should be appreciatedthat measuring DP between ambient air and the interior space using fixedapertures is not the only way to determine air flow in the system. Anyof numerous techniques may be used for measuring air flow to determinerespiratory flow rate. In some embodiments air flow may be measured bydirecting air to flow through a permeable screen. In some of theseembodiments, the flow resistance properties of the screen convert flowto DP, and in some embodiments the measurement of DP can be used toestimate flow. In some embodiments, air flow may be measured by a smallturbine or rotating fan that turns as air flows through it, for exampleby measuring the rate at which the turbine turns. In some embodiments, aheated element may be placed in the flow path, and its temperature orrate of heat loss can be used to measure air flow. In some embodiments aVenturi element is configured in the flow path of the air to measure theflow rate, using the Venturi principle. Any suitable technique formeasuring flow may be used, as embodiments of the invention are notlimited to employing any particular technique. Considerations outlinedabove for the air flow measurement can be applied or translated to othertechniques by individuals skilled in the art.

System Operation—Composition of Exhaled Air. The respiratory consumptionof oxygen over time is the cumulative difference between inhaled oxygenand exhaled oxygen over that time. The relative concentration of oxygenin ambient (inhaled) air is usually stable and rarely deviatessignificantly from its atmospheric vale of ˜20.95%. Similarly, therespiratory release of CO₂ is the difference between exhaled amount andinhaled amount, but CO₂ concentrations in ambient (inhaled) air arenegligibly low—typically 0.04% outdoors and usually no more than 2-3times higher indoors, which is still negligible compared with about 4-5%CO₂ that is typical of exhaled air, and for most purposes can beignored. In some embodiments, the fixed composition of inhaled air canbe used in various ways to facilitate the quantification of respiratorygas exchange.

In certain embodiments, inhaled air and exhaled air may constantly mixand replace each other in the interior space of the mask. Differentapproaches can be used to separately determine exhaled air compositionin such embodiments, and several non-limiting examples are describedherein: (a) Isolating a separate stream of exhaled air and measuring itscomposition, an approach referred to herein as “Separated Exhaled AirSensing” (SEAS), (b) Measuring the composition of a balanced mix of bothinhaled and exhaled air in the mask and mathematically extracting theaverage value of oxygen and CO₂ concentrations in the exhaled air, whichis referred to herein as “Mixed Air Sensing” (MAS), and (c) Usingsensors with sufficiently fast response time to measure rapid changes inconcentration and correlate measured concentrations with the respiratorycycle to isolate the properties of exhaled air, which is referred toherein as “Time Resolved Air Sensing” (TRAS). A more detailed discussionof these techniques follows. Beyond these example, other suitablemethods may be used with appropriate adjustments to the system itselfand the data analysis.

Separated Exhaled Air Sensing (SEAS). FIG. 7A shows a schematic view ofa representative technique and apparatus for performing SEAS. In theexample shown, a mask (700) is configured with apertures (760) and asensing module (710) attached to the mask. The sensing module comprisesa selective flow element (730) which allows air to flow from the maskinterior (720) to the module's sensing zone (740), but not the otherway. In this embodiment the selective flow element is “upstream” fromthe sensing zone, where “upstream” should be understood in reference tothe flow direction during exhalation. Flow may be further facilitated byan optional exit aperture (722) allowing air to flow out of the sensingzone as more exhaled air comes in. FIG. 7B adds arrows to depict airflow during exhalation, when the pressure P_(i) in the mask interior ishigher than the pressure in the ambient P_(a), namely DP is positive.Exhaled air exits the mask, primarily through the mask apertures (760),but also some exhaled air flows through the selective element (730) intothe sensing zone (740). In the example shown, some air from the sensingzone flows out to the ambient through the exit aperture (722).

In the same embodiment during inhalation, the interior pressure is lowerthan the ambient, namely DP is negative, shown in FIG. 7C. In theexample shown, this causes the selective flow element (730) to blockflow and prevent substantial ingress of ambient outside air into thesensing zone. The result is that over the course of one or morerespiratory cycles, the sensing zone continuously senses exhaled air andnot a mix of exhaled air and ambient air.

In some embodiments, the amount of exhaled air entering the sensing zoneduring exhalation may be only a small fraction of the total exhaled airand may not be constant. In some embodiments that fraction is less than1%. In some embodiments the fraction is between 1% and 10%. In someembodiments the fraction is not constant and varies with exhalation flowrate and volume. In some embodiments a significant portion of theexhaled air flows through the sensing zone. In some embodiments the FFvs DP relationship may be calibrated to take into account the amount ofexhaled air flowing to the sensing zone.

In some embodiments which employ SEAS, a selective flow element mayalso, or alternatively, be located “downstream” of the sensing zone. Onenon-limiting example is near the sensing zone exit aperture (722). Thiselement may prevent ambient air from entering the sensing zone when thepressure differential is reversed under inhalation. In some embodimentsthe selective element in (722) may be placed in addition to an elementlocated upstream (730), between the mask and the sensing zone, wherebythe sensing zone is effectively “sandwiched” between two selective flowelements.

Any suitable type(s) of element(s) may be used to selectively permit airflow, whether now known or later developed. In some embodiments, theelements are passive one-way flow valves. One example of such a valvecomprises a flexible flap configured to cover an aperture in such a waythat pressure and flow in the “open” direction pushes the flap aside andallows air passage, and pressure from the other direction tightens theflap to seal the aperture.

Some embodiments may employ electrically controlled active selectiveflow elements that are synchronized or coordinated with the DP sensorreadings so as to open for air flow only during exhalation, asdetermined by the positive DP. The mechanism can be piezoelectric,magnetic, electrostatic, or use any electric motor or actuator. In someembodiments, such active control allows the system to be programmed tovary the size of certain apertures and/or the amount of time thatcertain apertures remain at a particular size. In some embodiments,active control of the selective flow apertures may be used to manage thetiming, duration or the amount of air entering the sensing zone, for anypurpose. In a non-limiting example, active control may be programmed tosample air selectively from a particular phase or stage in eachbreathing cycle. In another non-limiting example, active control may beprogrammed to compensate for changes in breathing rate by increasing theopening during slow breathing or decreasing it during heavier breathing.

In some embodiments the sensors of the sensing zone are in fluidcommunication with the exhaled air entering the sensing zone, andprovide multiple readings at some frequency, which readings are passedto digital components of the electronic circuit, including but notlimited to a microprocessor, which may process, store, and/or transmitthe readings (and/or other information, including results of processingthe readings) to one or more external devices. In some embodiments thereading frequency may be between 30-60 per minute. In some embodimentsthe reading frequency may be less than 30 per minute. In someembodiments the reading frequency may be higher than 60 per minute. Inthis respect, the benefit of an increased reading frequency may bediminished by a number of factors, including but not limited to (a) aninherent response time of a gas sensor, (b) a diffusion or mixing timeof exhaled air entering the sensing zone, and (c) longer time constantsassociated with the physiology of certain biometric variables.Regardless, it should be appreciated that readings may be performed atany suitable reading frequency. It should further be appreciated thatembodiments of the invention are not limited to employing therepresentative apparatus and/or technique shown in FIGS. 7A-7C toperform SEAS, as any suitable apparatus may be used, to perform anysuitable technique(s) relating to measuring separated exhaled air. Somevariations on the representative apparatus and technique shown in FIGS.7A-7C are described below, and involve minimizing humidity, and the useof a vestibule. However, any of numerous other variations may beperformed. Embodiments of the invention are not limited in this respect.

Humidity Condensation. Because exhaled air has high relative humidity(RH) and water content, and because exhaled air is often warmer than theambient and the module components, some embodiments may employtechniques for minimizing the condensation of water on parts of themodule, which over time may interfere with their proper operation. Insome embodiments, water condensation may be minimized by limiting theamount of exhaled air passing through the module, such as by configuringthe components that direct exhaled air to the sensing zone. In someembodiments, the amount of exhaled air passing through the module may becontrolled at least in part by active flow elements.

Other techniques can be implemented to mitigate condensation, includingbut not limited to (i) incorporating desiccants or hydrophobic materialsto protect sensitive components and (ii) elevating the temperature ofsome parts of the module. In some embodiments heat from the exhaledbreath or the skin is transferred to elevate the temperature of parts ofthe module. In some embodiments the heat transfer is facilitated by oneor more heat transfer elements, a non-limiting example of which is ametallic surface embedded in the module housing and facing the interiorof the mask.

Vestibule. In some embodiments, a vestibule, as described above withreference to FIG. 5, may receive exhaled air prior to it reaching thesensing zone. In the example shown in FIG. 5, an inlet (510) allowsexhaled air to enter the vestibule space (500), and a first aperture orchannel (530) allows air to flow from the vestibule to the sensing zone(540). In some embodiments the vestibule can be further configured withone or more separate outlets (550) that may allow exhaled air to flow tothe ambient air. In some embodiments a vestibule may comprise selectiveflow elements in at least one of (510) and (550), configured to enableonly exhaled air to flow into the vestibule, from which it can alsodiffuse or flow into the sensing zone. In some embodiments, anyaperture, including (510) and (530) may further comprise a filter toprotect the sensing zone from ingress of particles, fluids orcontaminants. In some embodiments the vestibule may be an integral partof the part of the mask, whereas in some embodiments the vestibule maybe part of the detachable module. The incorporation of a vestibule intothe module may provide several advantages, including but not limitedacting as a buffer space, or allowing large variations in the amounts ofexhaled air to flow through vestibule, depending on the breathing rate,while maintaining relatively small flow of air into the sensing zone.

Mixed Air Sensing (MAS). In some embodiments the system is configuredsuch that the sensing zone is exposed to both inhaled air and exhaledair in similar amounts or at a known ratio between inhaled and exhaledair entering the sensing zone. FIG. 8 is a schematic view depicting arepresentative apparatus and technique for MAS, where an aperture (830)is configured between the mask interior space (820) and the sensing zone(840). In the example shown in FIG. 8, the opening (830) is notdirectionally selective and air can pass in either direction at any timeincluding during inhalation and exhalation, although the use of MAS doesnot necessarily preclude the use of selective flow elements. In someembodiments the opening may be protected with a permeable screen orfilter (832). The air composition reaching the plurality of sensors mayvary over the course of each breathing cycle, but, in certainembodiments, the time-averaged composition is a mix of substantiallyequal amounts of inhaled and exhaled air.

In some embodiments the concentration sensors are substantially linearin the range of interest between inhaled and exhaled air, whereby thevalue X of a specific gas component concentration (e.g. oxygen, CO₂,humidity) averaged over a breathing cycle can be determined by averagingthe corresponding sensor readings over the cycle:

$\left\langle X \right\rangle = \frac{\int_{0}^{T}{{X(t)}{\partial t}}}{T}$

And if the exposure to inhaled and exhaled air is quantitativelybalanced, then

$\left\langle X \right\rangle = \frac{X_{i} + \left\langle X \right\rangle_{e}}{2}$

Where the constant value for inhaled (ambient) air X_(i) isapproximately known, or alternatively is established by baselinecalibration procedure. As explained earlier, ambient oxygen can besimply approximated to be its known typical value in atmospheric air,and ambient CO₂ can similarly be approximated based on known values,which are practically negligible. In some embodiment humidity can be apart of some biometric calculations, and in some embodiments a separatehumidity sensor measures ambient humidity. The mixed-air measurement canbe used to extract exhaled values simply as follows:

(X)

_(e)=2

X

−X _(i)

In some embodiments, the amount of inhaled and exhaled air entering thesensing zone over each cycle are not equal. The formula can begeneralized to mixed air sensing where these are not equal but theirratio is known or may be approximated. In some embodiments it can alsobe generalized to account for non-linearity of one or more sensors. Insome embodiments, the ability to impute the exhaled air composition fromthe mixed air measurements can enable some simplifications in thephysical design of the MAS system. One non-limiting example is theelimination of a selective flow element from the air path between theinterior and the sensing zone. It should be appreciated that theapparatus and technique shown in FIG. 8 is merely exemplary, and thatany suitable apparatus and/or technique(s) may be used to perform mixedair sensing. Embodiments of the invention are not limited in thisrespect.

Time-resolved Air Sensing. In some embodiments the gas sensors may notrely on physical mixing or physical separation of inhalation andexhalation, but on fast-resolution readings of the air composition. Insome embodiments the sensor readings may be collected continuously alongwith the DP readings, which allows the system to associate themseparately with inhalation or exhalation; in some embodiments,exhalation corresponds to positive DP in the interior relative to theambient, while negative DP corresponds to inhalation. In someembodiments the exhaled air concentration values can be averaged toobtain the values required for biometric calculations. In someembodiments a certain (e.g., predetermined) time delay can be taken intoaccount between the onset of positive DP and the inclusion of sensorreadings for the purpose of representing exhaled air, this delayrepresenting, for example, a combination of one or more of (i) intrinsicsensor response time; (ii) flow or diffusion time in sensing module;(iii) displacement of ambient air in the interior at the end ofinhalation, or any other source of delay including physiological. Itshould be appreciated, however, that any suitable technique(s) may beused to perform time-resolved air sensing. Embodiments of the inventionare not limited in this respect.

Ambient Conditions. In some embodiments the ambient conditions includingbut not limited to any of temperature, barometric pressure and humidity(absolute or relative) may be measured by the system. These values canbe used for any number of biometric calculations. A non-limiting examplewould be to correctly relate volume and mass of air flow, as the massdensity of the air varies with barometric pressure (P) and temperature(T). Generally, the density of a gas, namely mass to volume ratio,increases with pressure and decreases with temperature, according to theideal gas law PV=nRT (where n is the amount of gas, in moles, and R isthe ideal gas constant). To convert gas volume to mass it is useful tomeasure, or to estimate, the ambient pressure (affecting both inhaledand exhaled air) and ambient temperature (primarily for inhaled air).The ambient pressure generally depends on altitude, and can further varywith weather patterns and can also be influenced, for example, by indoormechanical ventilation systems. Naturally temperature will vary betweenindoors, outdoors and weather or climate conditions. In someembodiments, ambient pressure and temperature are obtained from anothersystem or network via wireless communication, including but not limitedto publicly available meteorological information and indoor climatemonitoring systems.

In some embodiments the relative composition and density of the ambient(inhaled) air may be used for computing certain respiratory andmetabolic quantities. In some embodiments, ambient air composition canbe estimated simply as the typical composition of dry atmospheric air,which is 20.95% oxygen, 0.04% CO₂, with the remainder mostly beingmetabolically inert nitrogen (˜78%) and argon (˜0.9%). These values canbe corrected for humidity, which itself can be approximated, and/orreceived from an external information source. In some embodiments,concentration properties of ambient air, including but not limited toconcentrations of oxygen, CO₂ or humidity, are measured by sensors thatare part of the system.

In some embodiments the sensing module comprises sensors in physicalcommunications with the ambient air, to determine P and T. These valuescan be updated at any suitable frequency. In some embodiments ambientproperties are measured when triggered by an action taken by the user.In some embodiments an ambient sensor can be thermally insulated fromexhaled breath or other sources of body heat.

In some embodiments the composition of the ambient air can be determinedby the sensing module when it is not exposed to respiration. As anon-limiting example, this can be part of a calibration procedure thatis run when the module is not attached to the mask, as shownschematically in FIG. 2, or when the mask is removed from the user'sface. In some embodiments the calibration procedure can be initiated bythe user, for example by pressing a button on the module, or byrequesting a calibration from a program that is in wirelesscommunications with the module.

In some embodiments the calibration of pressure can be substituted witha determination of altitude which can be provided, for example, bysatellite based global positioning system (GPS), a cellular network oran external barometer. In some embodiments the GPS receiver can beincorporated into the subassembly itself. In other embodiments thesystem can rely on a mobile phone or another wireless device todetermine the altitude or pressure through its own GPS capability,barometer, or other means of determining altitude.

Other Sensors. Additional sensors can be added to detect other physicalor biometric parameters of interest that can complement the biometricinformation imputed from the analysis of the breath. In someembodiments, other molecular components of the exhaled air, includingketones, alcohols, ammonia or any other chemical species can be measuredby incorporating suitable sensors into the sensor subassembly. In someembodiments electrochemical sensors are used to detect certain molecularspecies, including alcohols, in breath. In other embodiments suitablesensors can trace ketones in the breath, which can be indicative ofketosis or diabetes. Ammonia can occur in breath in association withkidney disease or liver disease.

In other embodiments, electronic, electro-optical and/ormicro-electro-mechanical (MEMS) sensors may be incorporated in thesystem to provide complementary biometric information, including but notlimited to heartbeat, blood properties, and motion or acceleration (suchas step counters for monitoring walking or running). In anotherembodiment a GPS receiver is incorporated into the system, allowing theuser to associate biometric data with physical location.

In some embodiments the accuracy of certain calorimetric data may beinfluenced by the accuracy of the air flow measurement. For example, theDP sensing may require accuracy over a wide dynamic range of potentialrespiratory flow rates that can be difficult to address with a singlesensor. In some embodiments, the system comprises multiple pressuresensors with different dynamic ranges or sensitivities to improveaccuracy. As a non-limiting example for illustrative purposes only, thesystem may have two sensors, one ranging up to 250 pascals, the otherhaving a wider dynamic range up to 2000 pascals but with lowersensitivity. When the user is sedentary and breathing slowly, typicalmask DP readings may be below 10 pascals throughout the breathing cycleand the higher range sensor readings are ignored. Under high exertion,readings may go above 250 pascals, where the lower scale sensor is offscale and ignored. In the range between, say 10 pascals and 250 pascals,the system may take a weighted average of the readings with the relativeweight varying with the reading values.

Mask Design Considerations. Protective breathing masks are known in theart, typically covering much of the face from the bridge of the nose tothe chin or the lower jaw. In certain instances these attach ratherfirmly to the face (to prevent air leakage around the mask edge) or incontact with the mouth, rendering them potentially uncomfortable forextended use and otherwise disruptive for the user. In some embodimentsof the current invention, the mask seals around the mouth and the baseof the nose, namely the bottom of the nasal ala and the nasal tip, asshown in FIG. 1B. This may keep the entire bridge of the nose uncoveredand visible, as well as the cheeks, chin and lower jaw. The user canapply the mask while wearing glasses and can speak comfortably.

The shell can be made of any suitable material including but not limitedto plastics, resins, composites, fiber based materials, metals, ceramicsand plant derivatives. In some embodiments, the shell is substantiallytransparent. In some embodiments, the shell is rigid and maintains itsform under ordinary usage. In some embodiments the firm structureprovides a robust DP vs FF relationship as explained earlier. In someembodiments the firm structure is configured to avoid contact with thelips and not impede speech. A thinner shell wall may generally providefor lower weight. In some embodiments a thin shell is reinforced withribs, spines or other skeletal and/or topographical features. In someembodiments the shell is water resistant. In some embodiments the shellcomprises a hydrophobic material or a hydrophobic surface treatment, forexample to reduce visible condensation of breath. In some embodimentsthe surface is textured for visual or aesthetic purposes.

The edge seal may be achieved with a soft, conforming, elastic orotherwise pliable material along the perimeter of the mask. The materialmay be configured to come into contact with the face and to at leastpartially conform to its contours. In some embodiments the edge materialis a silicone rubber flap, cushion or gusset. Different types ofsilicone rubber with different mechanical properties can be used in thesame mask, for example to provide more softness or pliability around thenose area where contours vary more significantly between differentusers. Other types of seal materials can be used including any suitablerubbers, foams or plastics. In some embodiments a natural or syntheticfiber-based material is used, such as fabric or paper. In otherembodiments an air-filled cushion is configured along the edge of themask, comprising a thin elastic material creating a tube or a cushioncontaining air.

FIGS. 9A-D show a number of non-limiting examples of mask apertureconfigurations. The breathing apertures in the shell can take anysuitable form, including but not limited to a plurality of holes of anydesired size or shape such as circular or polygonal holes; any othersuitable form may be used. In some embodiments, such as FIG. 9B, theapertures can form an array of numerous small holes. In some embodimentsthe mask has multiple apertures of different shapes or dimensions. Inother embodiments the apertures can be a plurality of elongated slits,including but not limited to a grille formed by parallel slits.Apertures can be located in the (hard) shell and in the (soft) cushionarea. In other embodiments the apertures can be stylized geometricallyfor any functional or aesthetic purpose.

In some embodiments the apertures can have structure that provides somedirectionality or distribution to the air flow, such as relative to themouth and nose or relative to the location of the sensing subassembly.This can be facilitated, for example, by tilted inner walls orprotrusions, similar to an air distribution grille common in heating andair conditioning systems. In other applications the distribution of airflow inside the mask is affected by air channels, protrusions or wingsinside the mask.

The relation between respiratory flow and DP readings can be influencedby the number and location of the apertures, as well as the flowpatterns of air inside the mask. In some embodiments, multiple, smallerapertures are used, rather than a few large ones, to minimizesensitivity to variations in breathing patterns. A non-limiting example,for illustration purposes, is shown in FIG. 9B. In certain embodiments,aperture location is designed to eliminate or reduce direct exhalationfrom reaching at least some of the apertures directly in laminar flow.In a non-limiting example, apertures are located near the edges of themask or at as much distance as practical from the mouth and nose. Anon-limiting example is shown in FIG. 9D. In other embodiments, a mesh,filter or any other type of air permeable screen is configured over anaperture. In some embodiments, the mask further comprises a plurality ofbarriers or shields in the interior space, that can disrupt flow insidethe mask, increasing turbulence or otherwise redistributing pressure andflow gradients more uniformly.

In some embodiments inhalation resistance may be reduced byincorporating one-way inhalation inlets. A non-limiting example is shownas (134) in FIG. 1A. In some embodiments, air flow is only determinedduring exhalation where the resistance generates higher (and thereforeeasier-to-measure) differential pressure. Conversely, other embodimentsmay provide lower exhalation resistance with one-way exhalation valves,and inhalation pressure may be relatively higher and easier to measure.

The mask can be attached to the face by any suitable apparatus. In someembodiments, one or more straps, laces or elastic bands behind the neckor the head hold the mask in place. In some embodiments, bands or strapsbehind the ears hold the mask in place. In some embodiments the mask isattached to a hat or head cover. In some embodiments the mask isattached to a harness around the head or the ears. In some embodimentsthe mask is “strapless,” held in place by an adhesive material oradhesive layer between the skin and parts of the mask.

Communications & Applications. In some embodiments, the sensing modulereceives readings from the pressure sensor, the gas sensors, and anyother sensors that may be included. The readings, or any calculatedquantities derived from the readings (collectively, the “data”) may bestored temporarily in electronic memory. In some embodiments, the modulemay transmit the data to one or more external receiving devices, whichmay receive the data and store it, analyze it, produce related reportsand/or visual outputs, and/or share it with other devices. An externaldevice can be a mobile computing device (e.g., a mobile phone,smartphone, tablet, gaming device, console, or wearable computingdevice), a stationary computer (e.g., a laptop computer, desktopcomputer, or server computer), and/or any other computing system,including a computing device which is embedded within a car or anothersystem. Communication to an external device may be accomplished usingany suitable communication protocol(s) and/or infrastructure, whethernow known or later developed. For example, in some embodiments, suchcommunication may be performed wirelessly, including but not limited tousing Bluetooth®, BLE® LoRa®, and WiFi. For example, in some embodimentsa Bluetooth® modem may be installed in the sensing module and transmitdata to a nearby external device such as a smart phone or hand-heldcomputer. In some embodiments, such communication may be wired. Anysuitable way(s) of communicating data to one or more external devicesmay be employed.

In some embodiments the sensing module may accrue, compress and/oraggregate data before sending it to an external device. Accrued and/oraggregated data may, for example, be transmitted periodically (e.g.,based on an amount of time having elapsed since a previous transmission)and/or based an amount of data having accrued. Additionally oralternatively, transmission of data may be initiated by a user or by anexternal receiving device.

Calorimetry and Biometrics. In some embodiments, sensor readingsincluding (but not limited to) one or more of DP, oxygen concentration,CO₂ concentration, humidity, temperature, and barometric pressure, areused as inputs to calculate preliminary quantities including respiratoryair flow (FF), oxygen consumption (VO2), and CO₂ production (VCO2). Insome embodiments, the preliminary quantities, along with certain sensorreadings, can be used to convert or calculate “secondary” metrics,including but not limited to breath count (total breaths taken),breathing rate (breaths per minute, BPM), cumulative breathing volume(e.g., liters), respiratory exchange ratio (RER=VCO2/VO2) over any timeinterval, metabolic energy released (i.e., calories “burned”), andapproximation of carbohydrates metabolized and fats or lipidsmetabolized (which can be expressed in grams or calories). In oneexample, carbohydrate metabolism is associate with an RER value of 1.0,whereas the average RER for typical lipids is approximately 0.7. In someembodiments a measured value of RER (between 0.7 and 1.0) can be used toimpute a utilization ratio of these two classes of metabolic fuels,which is typically accurate as long as there is no significant energymetabolism using proteins. These and other biometrics can be calculatedas instantaneous values and rates, or as cumulative or average valuesover a certain period.

The physiology underlying these biometrics is relatively well known tomedical science, and some of the conversion formulas can be found in anynumber of texts (for example, “West's Respiratory Physiology” by J. B.West and A. M. Luks, 10^(th) ed., 2016; or “Energy Metabolism, Indirectcalorimetry, and Nutrition” by S. Bursztein. 1989 Lippincott Williams &Wilkins). However, as noted above, the actual measurement of respiratorybiometrics has thus far been restricted to laboratories, clinics orprofessional settings with complex, cumbersome and expensive equipment.

In some embodiments one or more calculations (e.g., relating tobiometrics) may be performed “on-board” the sensing module itself. Insome embodiments, one or more calculations may be performed by anexternal device, using data transmitted to a receiving device by thesensing module. In some embodiments, one or more calculations may beperformed by a computing system that is not in direct communication withthe sensing module (e.g., using data which is provided by one or moreintermediate devices). Embodiments of the invention are not limited tobeing implemented in any particular way.

Generality. Having thus described several aspects of at least oneembodiment of this invention, it is to be appreciated that variousalterations, modifications, and improvements will readily occur to thoseskilled in the art. Such alterations, modifications, and improvementsare intended to be part of this disclosure, and are intended to bewithin the spirit and scope of the invention. Further, though advantagesof the present invention are indicated, it should be appreciated thatnot every embodiment of the invention will include every describedadvantage. Some embodiments may not implement any features described asadvantageous herein and in some instances. Accordingly, the foregoingdescription and drawings are by way of example only.

Various aspects of the present invention may be used alone, incombination, or in a variety of arrangements not specifically discussedin the embodiments described in the foregoing, and it is, therefore, notlimited in its application to the details and arrangement of componentsset forth in the foregoing description or illustrated in the drawings.For example, aspects described in one embodiment may be combined in anymanner with aspects described in other embodiments.

The invention may be embodied as a method, of which various exampleshave been described. The acts performed as part of the method may beordered in any suitable way. Accordingly, embodiments may be constructedin which acts are performed in an order different than illustrated,which may include different (e.g., more or less) acts than those whichare described, and/or which may involve performing some actssimultaneously, even though the acts are shown as being performedsequentially in the embodiments specifically described above.

Use of ordinal terms such as “first,” “second,” “third,” etc., to modifyan element does not by itself connote any priority, precedence, or orderof one claim element over another or the temporal order in which acts ofa method are performed, but are used merely as labels to distinguish oneelement having a certain name from another element having the same name(but for use of the ordinal term) to distinguish the elements.

Also, the phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having,” “containing,” “involving,” andvariations thereof herein, is meant to encompass the items listedthereafter and equivalents thereof as well as additional items.

What is claimed is:
 1. A method for determining a concentration (X_(e))of a gas component in breath exhaled by a subject, the method being foruse in a system comprising a flow path through which flows air exhaledby the subject and air to be inhaled by the subject, the flow pathcomprising at least one sensor configured to measure the concentrationof the gas component, the method comprising acts of: (A) receiving aplurality of readings by the at least one sensor of the concentration ofthe gas component; (B) based at least in part on the plurality ofreadings, determining a time-averaged value X of the concentration ofthe gas component; (C) based at least in part on the time-averaged valueX of the concentration of the gas component, determining theconcentration X_(e) of the gas component in air exhaled by the subject;and (D) determining at least one respiratory or metabolic valueconcerning the subject based at least in part on the determinedconcentration X_(e) of the gas component.
 2. The method of claim 1,wherein determining the concentration X_(e) in the act (C) employs alinear function of X comprising a multiplicative coefficient of X equalto 2, reflecting similar amounts of exhaled and inhaled air beingexposed to the at least one sensor over the time period.
 3. The methodof claim 1, wherein determining the concentration X_(e) in the act (C)employs a linear function of X comprising a multiplicative coefficientof X that is not equal to 2, reflecting an asymmetry in amounts ofexhaled and inhaled air being exposed to the at least one sensor overthe time period.
 4. The method of claim 1, wherein determining theconcentration X_(e) in the act (C) employs a linear function of Xcomprising subtraction of a constant X_(i) associated with apredetermined concentration of the gas component in ambient air.
 5. Themethod of claim 1, wherein the gas component is one of oxygen and carbondioxide.
 6. A method for enabling determination of a concentration(X_(e)) of a gas component in exhaled air without separating the exhaledair from inhaled air, method comprising acts of: (A) providing a sensingspace configured so as to be in fluid communication with both airexhaled by a subject and air to be inhaled by the subject, such that,when employed by the subject, the sensing space contains a mix of theair exhaled by a subject and air to be inhaled by the subject; (B)providing at least one sensor in fluid communication with the sensingspace; and (C) providing at least one processor programmed to: receivereadings by the at least one sensor of the concentration of the gascomponent; determine a time-averaged value X of the concentration of thegas component; and determine, based at least in part on thetime-averaged value X, the concentration X_(e) of the gas component inair exhaled by the subject.
 7. The method of claim 6, wherein the atleast one processor is programmed to determine the concentration X_(e)using a linear function of X comprising a multiplicative coefficient ofX equal to 2, reflecting similar amounts of exhaled and inhaled airbeing exposed to the at least one sensor over the time period.
 8. Themethod of claim 6, wherein the at least one processor is programmed todetermine the concentration X_(e) using a linear function of Xcomprising a multiplicative coefficient of X that is not equal to 2,reflecting an asymmetry in amounts of exhaled and inhaled air beingexposed to the at least one sensor over the time period.
 9. The methodof claim 6, wherein the at least one processor is programmed todetermine the concentration X_(e) using a linear function of Xcomprising subtraction of a constant X_(i) associated with apredetermined concentration of the gas component in ambient air.
 10. Themethod of claim 6, wherein the gas component is one of oxygen and carbondioxide.
 11. A system for enabling determination of a concentration(X_(e)) of a gas component in exhaled air without separating the exhaledair from inhaled air, the system comprising: at least one sensorconfigured to measure a concentration of the gas component in mixedrespiratory air comprising exhaled air and ambient air; and at least oneprocessor programmed to receive readings by the at least one sensor ofthe concentration of the gas component in the mixed respiratory air,determine a time-averaged value X of the concentration of the gascomponent, and determine, as a linear function of X, the concentrationX_(e) of the gas component in air exhaled by the subject.
 12. The systemof claim 11, wherein the at least one processor is programmed todetermine the concentration X_(e) at least in part by producing aproduct by multiplying X by 2, and subtracting from the product aconstant X_(i) approximately equal to a concentration of the gascomponent in ambient air.
 13. The system of claim 11, wherein the atleast one sensor comprises an oxygen sensor.
 14. The system of claim 11,wherein the at least one sensor comprises a CO₂ sensor.
 15. The systemof claim 11, comprising a mask to which one or more of the at least onesensor and the at least one processor is attached.